With the increasingly strict regulations on emission, exhaust gas recirculation technology has been applied in power unit more widely and the EGR coolers of various structures have been invented in succession. Among them, the plate-fin EGR cooler has gained more popularity due to its excellent heat dissipation performance.
The increasingly strict regulations on emission drive the improvement of the EGR rate, namely, the exhaust gas flow needed to be cooled by the EGR cooler is on the increase. Besides, many EGRs are set before the turbo, making them high-pressure EGRs which results in the exhaust gas temperature entering the EGR cooler reaching 700° C.-800° C.
A regular plate-fin EGR cooler is an exhaust gas recirculation cooler and its turbulent cooling fins disclosed by Chinese patent CN2009201173214. As shown in FIGS. 11, 12 and 13, the EGR cooler includes an air inlet pipe 1′, an inlet chamber 2′, a core assembly 5′, a discharge chamber 6′ and an air outlet pipe 7′ which are connected in sequence. The core assembly 5 includes a turbulent cooling fin 11′, a flat cooling pipe 10′, a connecting main board 9′, a shell 4′, a water inlet pipe 3′ and a water outlet pipe 8′. Multiple flat cooling pipes 10′ are mounted by layers in the shell 4′ with two ends of them plugged and fixed in holes on the main board 9′ and connected to the inlet chamber 2′ and the discharge chamber 6′. The turbulent cooling fins 11′ are equipped in each flat cooling pipe 10′. The two connecting main boards 9′ are respectively fixed at the two ends of the shell 4′. The water inlet pipe 3′ and the water outlet pipe 8′ are equipped on the shell 4′.
The gas channel of the EGR cooler is composed of several flat pipe units. A single flat pipe unit is consisted of a flat pipe 10′ and its built-in heat transfer fin 11′. Each flat pipe unit is welded to the corresponding hole of the main boards 9′ to make a core assembly. The two main boards 9′ of the core assembly are welded with the shell 4′, the inlet chamber 2′ and the discharge chamber 6′. The water inlet pipe 3′ and the water outlet pipe 8′ are welded to the shell 4′ to form the EGR cooler assembly. Thus, the exhaust gas is flowing at the inner chamber of the flat pipe unit and the cooling water is flowing at the external side of the flat pipe unit and the internal cavity of the shell 4′, absorbing heat of the exhaust gas and taking the heat away.
The regular plate-fin structure EGR cooler has the following disadvantages: 1. when the EGR cooler is in operation, the high-temperature exhaust gas impact the main board of the EGR cooler and the main board will expand to generate stress; 2. during the operation of the EGR, the different expansion and contraction of the shell and the flat pipe unit result in axial stress. The stress generated due the above two points can easily lead to the cracking of the welded joint at the ends of the main board and the flat pipe unit.